The protein kinase SOS2 activates the Arabidopsis H(+)/Ca(2+) antiporter CAX1 to integrate calcium transport and salt tolerance

J Biol Chem. 2004 Jan 23;279(4):2922-6. doi: 10.1074/jbc.M309084200. Epub 2003 Oct 28.


The regulation of ions within cells is an indispensable component of growth and adaptation. The plant SOS2 protein kinase and its associated Ca(2+) sensor, SOS3, have been demonstrated to modulate the plasma membrane H(+)/Na(+) antiporter SOS1; however, how these regulators modulate Ca(2+) levels within cells is poorly understood. Here we demonstrate that SOS2 regulates the vacuolar H(+)/Ca(2+) antiporter CAX1. Using a yeast growth assay, co-expression of SOS2 specifically activated CAX1, whereas SOS3 did not. CAX1-like chimeric transporters were activated by SOS2 if the chimeric proteins contained the N terminus of CAX1. Vacuolar membranes from CAX1-expressing cells were made to be H(+)/Ca(2+)-competent by the addition of SOS2 protein in a dose-dependent manner. Using a yeast two-hybrid assay, SOS2 interacted with the N terminus of CAX1. In each of these yeast assays, the activation of CAX1 by SOS2 was SOS3-independent. In planta, the high level of expression of a deregulated version of CAX1 caused salt sensitivity. These findings suggest multiple functions for SOS2 and provide a mechanistic link between Ca(2+) and Na(+) homeostasis in plants.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Antiporters / metabolism*
  • Arabidopsis / enzymology*
  • Arabidopsis Proteins
  • Calcium / metabolism*
  • Calcium-Binding Proteins / metabolism*
  • Cation Transport Proteins / metabolism*
  • Enzyme Activation
  • Ion Transport
  • Plant Proteins / metabolism
  • Protein Serine-Threonine Kinases / metabolism*
  • Sodium / metabolism


  • Antiporters
  • Arabidopsis Proteins
  • Calcium-Binding Proteins
  • Cation Transport Proteins
  • Plant Proteins
  • calcium-hydrogen antiporters
  • Sodium
  • SOS2 protein, Arabidopsis
  • Protein Serine-Threonine Kinases
  • Calcium